This story literally hits the ground running, with our hero White Jackson hunting a Amsir (the indefinite article is a foible of his dialect) across a desert. He must stay within sight of the Iron Thorn, a clearly ancient man-made tower, or he won't be able to breathe. This limited environment is the first microcosm that Jackson explores and then abandons. His small tribe huddling around the Thorn with their frozen culture do not satisfy him, and in due course he breaks away to the next worldlet on his journey, the city of the flying Amsirs themselves.
It is less these imagined societies than Jackson himself that forms the subject matter of the book. Jackson's other names change several times, reflecting his restless inability to conform to social roles. He has no time for fakery, tradition or authority, ultimately finding even the world of the Thorn's creators a pointless mummers parade. Incidentally an accomplished artist, he has perhaps too sharp an eye for reality for his own good: "To me I am the only sane man conceivable."
Budrys is a neglected but very fine writer of SF, and even his lesser works, like this one, have a distinctive metaphysical edge. Here he shows us a rational man who will brook no nonsense, a modern post-Enlightenment man despite his upbringing in a backward society, and shows us too how that admirable hunger for truth makes peace of mind impossible. A far-future "Catcher In The Rye", it's a tight, thoughtful, slightly worrying book.